Biomechanical Modeling: Using high speed videolaryngoscopy and analysis of the movement trajectories from the arytenoid cartilages, two models of cricoarytenoid joint action were evaluated. Support was found only for the model of rotation around the long axis of the cricoid articular facet. High resolution anatomical data on cadaveric human larynges are being obtained through MRI scanning with a 2 Tesla 30 cm bore scanner. The images are being segmented to develop 3 dimensional representations of the cartilages and muscles. Modulation of Laryngeal Sensori-Motor Responses: While stimulating the superior laryngeal nerve percutaneously, the effects of task performance, phonation and effort closure, on R1 and R2 sensori-motor responses, were studied in normal awake humans. Although R2 became reduced during these activities, R1 seemed unaffected by task performance. The results suggest that modulation of these responses may not take place at the brain stem level but by affecting afferent response characteristics. Neurophysiological Studies of Patients and Controls: Studies of laryngeal muscle activation in adductor spasmodic dysphonia did not find muscle hyperactivity when patients were not producing speech or when they were producing speech but did not have voice symptoms. The thyroarytenoid muscle was hyperactive only during speech symptoms. Treatment of Abductor Spasmodic Dysphonia: Botulinum toxin injections into the posterior cricoarytenoid muscles have proved beneficial in only a small proportion of the patients with abductor spasmodic dysphonia.